Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.54   4.296%   $65.2267   $65.23   $65.25   $65.20  
  Purchase #2 $202.34   8.428%   $219.3932   $219.39   $219.40   $219.40  
  Purchase #3 $47.37   7.634%   $50.9862   $50.99   $51.00   $51.00  
  Purchase #4 $152.34   9.676%   $167.0804   $167.08   $167.10   $167.10  
  Purchase #5 $207.62   6.632%   $221.3894   $221.39   $221.40   $221.40  
  Purchase #6 $112.48   11.333%   $125.2274   $125.23   $125.25   $125.20  
  Purchase #7 $130.86   4.464%   $136.7016   $136.70   $136.70   $136.70  
  7 purchase totals = $915.55       $986.0049   $986.01   $986.10   $986.00